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Parameters of the Green-Ampt equation can be estimated either by calibration or from information available from soil survey data. Methods have been developed by to determine parameters from laboratory measurments of water content, soil porosity, residual saturation, bubbling pressure, and pore size. In lieu of detailed measurments, the following parameter estimates can be used based on soil texture classes: GREEN.AMPT PARAMETERS , TOTAL POIlOSITY WETTED FRONT HYDRAUUC SOIL TYPE SUCTION CONDUCTIVITY p wflinl k linlhrl Sand 0_437 1.95 4.135 Loamy Sand 0.437 2.41 1.205 Sandy Loam 0.453 4.33 0.510 Loam 0.453 3.50 0.260 Silt Loam 0_501 6.57 0.135 Sandy Loam Clay 0.398 8.60 0.085 Clay Loam 0.464 8.22 0.046 Silty Clay Loam 0.471 10.75 0.033 Sandy Clay 0.430 9.41 0.025 Silty Clay 0.479 11.50 0.018 Clay, 0.475 12.45 0.012 It should be noted that for totally dry initial conditions, total porosity minus water content is equal to effective porosity, which is generally about 75 to 97 percent of the total porosity. 8. FIELD MEASUREMENT OF INFILTRATION. Although many methods can and have been used to measure infiltration rates in the field, a common practice is through the use of a double ring infiltrometer. These consist of concentric cylinders approximately 40 cm high. Diameter of the inner ring is 28-33 em, while the outer ring is 50-60 cm in diameter. Concentric rings are used, with measurement confined to the inner ring, in order to minimize error due to flow divergence in directions other than the vertical. In the field, the cylinders are driven into the soil surface to approximately 15 cm of depth. Water is filled to a depth of about 10 cm in both cylinders and the time and height of water in the inner cylinder are recorded. Measurements are taken at 10, 20, 30, 45, 60, 90 and 120 minutes 7-8